The broadband network may be based on the LTE (“Long Term Evolution”) technology or the mobile WiMAX “Worldwide interoperability for Microwave Access”) technology and support radio links with the mobile terminals of the orthogonal frequency multiplexing multiple access OFDMA (“Orthogonal Frequency Division Multiple Access”) type, and of the single carrier frequency multiplexing multiple access SC-FDMA (“Single Carrier Frequency Division Multiple Access”) type.
Radio resources of traffic offered both in the frequency field and the time field are limited by the frames configured in a base station of such network of the general public type and are shared in a variable way between active radio links with the mobile terminals under the coverage of the base station. The service qualities, including in terms of flow-rate, are variable as a function of the various types of communications with mobile terminals. The base station should permanently adapt dynamically to the characteristics of the services being offered to mobile terminals and requested by the latter. When an application in the base station or in a mobile terminal requires radio resources, the station allots to it resources selected amongst the available resources in the frames while trying to meet the amount of required resources. The base station then periodically modifies in the frames the allotment of resources to the communications with the mobile terminals as a function of their needs in resources. The position in frequency and in time of the resources allotted to a link with a mobile terminal in a downward or upward radio frame is not strictly determined and may change from one frame to the next one. For instance, resources spreading on a few sub-carriers in a narrow band and a few consecutive periods of symbols defining a block of resources having a determined position in a frame are allotted to a terminal in a frame and are allotted to another terminal in a subsequent frame. According to another example, the base station allots to a terminal block of resources in a frame and a block of resources having a position different from the previous one in a subsequent frame. Consequently, a block of resources having a determined position in a frame might be allotted a priori to any of the mobile terminals.
Moreover, although the frequency band is broad, the resources in a frame are limited and the base station is sometimes unable to access all the communication requests with the mobile terminals or all the service qualities of the communications.
Furthermore, it is known to use for services of critical mission of public security a professional private terrestrial narrow band radio communications network PMR (“Professional Mobile Radio”) for instance of the DMR type ((“Digital Mobile Radio”), TETRA “Terrestrial Trunked Radio”) or P25 with digital cellular radio interfaces based, more specifically, on the IP protocol (“Internet Protocol”). It is also known to gather stationary and mobile terminals by groups in the professional private network so that any terminal member of a group is able to transmit vocal data, or sometimes short messages at higher flow-rates, to other terminal members of the group through the infrastructure of the network and to receive data from any other terminal belonging to the group through the infrastructure of the network. The stationary and mobile terminals of a group can only communicate therebetween. Sharing radio resources (“trunking”) in a base station of the professional private network is carried out in the shape of channels, the number and the flow-rates of which are determined, so as to safely meet the needs in resources of communications and in radio coverage of the mobile terminals.
The use constraints of the professional private network, as reliably establishing all the communications needed for operating a group of terminals so that all the members of this group are able to permanently communicate therebetween data including vocal ones, are not compatible with the variable and dynamic and thus, unsure, allotment, of the radio resources offered by a base station in a broadband network of the general public type, and with the resetting of the allotment of the order of the millisecond, either every frame or every sub-frame of each frame, in the base station.